As stated in U.S. Pat. No. 3,795,517, this invention relates to an electro-optic display device which is improved in reference thereto by the use of multiple heterojunctions of photoconductive layers as to allow high speed reproduction of image on a display such as a liquid crystal.
The prior art shows that one may be using both photoconductive and liquid crystal materials produce an image by projecting light thereon when pulsing with a voltage applied to transparent electrodes connected to said materials. As stated in the aforesaid patent and summarized in U.S. Pat. No. 3,824,002 in reference thereto such structure is to switch the voltage that drives it from the photoconductive material to the liquid crystal material under command of a light source.
In such prior art devices, the photoconductive layer ranged between 1 to 25 microns and had a resistance of about 10.sup.10 ohms-centimeters. This layer was then controlled by a light source in that the amount of illumination directed onto such a photoconductive layer determined the amount of current flowing through it between the electrodes. In other words, by becoming selectively conductive, a photoconductor can control the excitation of an electro-optic device. Typically, the prior art uses of such structures was to create a conductivity image corresponding to images created by almost any form of light energy radiated thereto.
It is in the improvement of these prior art devices that this invention finds utility.